ENGR 101/ HUM 200: Technology & Society

1. ENGR 101/ HUM 200: Technology & Society November 2, 2005

2. Agenda • Mid-quarter feedback • Exam Rescheduled for Tuesday 11/8 • Project comments (Thursday class; Define “better,” clearly define target users, if interviewing or testing them, how identify or recruit them, multiple ways to prototype) • International perspectives on energy consumption • Renewable energy

3. International Issues • Developing world energy sources • About one-third of world’s population lacks access to modern energy sources • Infrastructure is a significant expense • Centralized technologies require enormous investments and maintanance • Bioenergy (wood and other plant matter derivatives) is a cornerstone of sustainable energy strategy

4. Biomass • Can contribute to deforestation • Labor intensive work of collecting firewood • Indoor smoke pollution • Examples: • Residues and waste • Purpose-grown energy crops • Natural vegetation • Agriculturally, balance out food and energy crops

5. Biomass Case Studies • Ethanol from sugarcane in Brazil • Sugarcane residue used for electricity generation • Corn stalk processing for cooking fuel in China • What infrastructure is required?

6. Solar Power • First explored by engineers over 100 years ago (not a byproduct of the US environmental movement in the 1970s!) • Appealed to people for use in Algeria and India • Early initiatives bypassed in favor of ease and cheap cost of coal and wood • Early parabaolic reflectors kept getting felled by weather • Decentralized technology. What infrastructure is required?

7. Three Technologies for Solar Power • Photovoltaic cells • Concentrating solar power technologies • Low-temperature solar collectors

8. Photovoltaic Cells • Convert sunlight directly into electricity (photo:volt) • Made of semiconductors such as crystalline silicon or various thin-film materials • Also known as solar cells (put together into modules and arrays) • Can provide anything from tiny amounts of power for watches to large amounts for the electric grid • A PV System includes electrical connections, mounting hardware, power-conditioning equipment, and batteries that store solar energy for use when the sun isn't shining • Current uses of PVs include communications satellites, water pumps, road and traffic signs

9. Photovoltaics: one cell produces 1 to 2 watts of power

10. Uses of Stand-alone PVs • Replacement energy when other utilities are: • Unavailable, undesirable (no tolerance for interruption), too costly to extend power lines • Can produce energy where and when it's needed, so complex wiring, storage, and control systems aren't needed • Small systems produce less than 500 watts and weigh less than 68 kilograms (150 pounds); easy to transport and install • Most installations take only a few hours and PV modules need only an occasional inspection and cleaning

11. Concentrating Solar Power Technologies (CSPs) • Use mirrors to concentrate the sun's heat energy • Drive a steam generator to produce electricity • Include dish/engine systems, parabolic troughs, and central power towers

12. CSPs • Relatively low cost and can deliver power when and where it is needed • Excellent for satisfying need for distributed source of energy • Can range from small-scale (village power, 10 kilowatts) to large-scale (grid-connected applications, 100 megawatts). • Can use thermal storage during cloudy periods or at night. • Can also be combined with natural gas • Amount of power generated depends on amount of direct sunlight. Good for sunbelt locations. • Enough electric power for the entire country could be generated by covering about 9 percent of Nevada—a plot of land 100 miles on a side—with parabolic trough systems.

13. Two Designs of CSPs • Troughs • Parabolic shaped reflectors concentrate the sun’s energy; pipe with oil runs down the middle and gets heated up by solar energy, which then generates electricity in a conventional steam generator • Power towers • Lots of large, sun—tracking mirrors that focus sunlight onto a receiver at the top of a tower; heat transfer fluid (steam, molten nitrate salt) in the receiver generates steam

14. Low-temperature Solar Collectors • Absorb the sun's heat energy • Heat is used directly for hot water or space heating for residential, commercial, and industrial facilities • Different kinds of collectors used based on need

15. Solar Case Studies • Boosting a telephone signal in Nevada • Providing water for cattle in South Dakota • Powering a modern home in Florida

16. Next class • Make It Better activity • Review of Amory Lovins video lecture • Exam scheduled for Tuesday the 8th. Review session will be Monday 5:30pm-6:30 pm